The Guardian's second social audit, in which it tests its own behaviour as an organisation against the demands it makes of others, is published this week at a time when the paper is engaged in what may prove to be the most momentous changes in its history.

The chief executive of the company and the editors of the Guardian and the Observer, in a joint introduction to the audit, refer to the present situation as a "crossroads". It is one from which the Guardian will go forward in a new format with its journalistic values essentially reinforced. The audit gives the fullest account the paper has offered so far of the thinking behind the "critical decision" to change to the so-called Berliner or midi format.

Trust is a recurring theme. Publication of the social, ethical and environmental audit itself represents an unusual act of trust in the context of an industry that in general is not highly trusted. The report points out that a Mori poll of 2,000 adults from earlier this year found that although trust in journalists had risen slightly to 20% they were still considered the least trustworthy of any group, including politicians. Against this, the audit reveals that in a poll of 2,500 readers and web users carried out in June this year 93% said they trusted the Guardian's editorial coverage (with the figures for the Observer and Guardian Unlimited 87% and 89% respectively).

The social audit suggests reasons for this in the degree of frank revelation it offers - unique among UK media organisations - and the involvement that it invites. There can be few media organisations anywhere that let you in so far and then tell you so much about themselves, including their identified faults. The independent auditor, whose job it is to report on the reliability of the inquiry said the Guardian was "not only providing a beacon for British media companies but setting standards in disclosure for the whole corporate sector".

The audit, which in fact, covers the whole of GNL - comprising the Guardian, the Observer and Guardian Unlimited - shows that to a remarkable degree the Guardian does practise what it preaches and that where it does not it is actively trying to do something about it: to close the gap between the aim and the actuality. It will be picked over for signs of complacency but its tone, I suggest, is pretty rigorous and invigorating.

The report examines: the paper's relationship with its readers and the way it responds to their queries and complaints (a survey of Guardian readers showed that 59% of you are now aware of the existence of the readers' editor); its relationship with its suppliers, who are expected to have social policies compatible with the Guardian's; and it considers the views of its staff, including their caveats about pay and conditions. Asked in 2003 whether they thought pay and conditions were fair across the whole of GNL only 15% agreed with the proposition that they were (48% thought they were not). However, asked in the same survey to respond to the statement "I am proud to work at GNL", 86% agreed that they were. The intention is to conduct these staff surveys every two years.

The audit pays particular attention to the paper's record on the environment. It says, "We pride ourselves on our environmental coverage and put more resources into this area than any other national newspaper." When professionals working for environment agencies were asked which of the UK quality newspapers provided the most authoritative coverage in this area 76% of them nominated the Guardian (none at all said the Times or the Daily Telegraph).

However, the audit concedes, "It is only in the past year that we as a company have started to consistently heed our own advice. We have now formulated a comprehensive environmental policy covering procurement, energy, water and waste management with a commitment to continuous improvement." Recycled paper now accounts for 75% of newsprint used by the Guardian and Observer - 93% of Guardian readers recycle their paper.

The spirit of the Scott Trust, the ultimate owner of the Guardian, permeates the report. The paper - in the words of CP Scott, quoted in the report by the trust's present chair - has "a moral as well as a material existence".